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| United States Patent |
6,228,530
|
|
Dokyu
, et al.
|
May 8, 2001
|
Dry cell and method of manufacturing outer metal jacket thereof
Abstract
Notches (21a, 21b) are formed at the corners of only one side edge (19a) of
a metal jacket blank (19) of a rectangular metal strip. The blank (19) is
rolled into a cylindrical shape so that its opposite sides (19a, 19b) are
adjoined to each other forming an abutment joint (10) and a lower end
(19c) of the blank (19) is inwardly curled and crimped to form a bottom,
thus completing an outer metal jacket (18). After a cell member (26) is
loaded into the metal jacket (18), the upper end (19d) of the blank (19)
is inwardly curled and crimped to cause the notches (21a, 21b) to abut the
other side edge (19b) of the blank (19), forming a curled abutment joint
(20) along a direction (S) which is different from the radial direction
(R) of the metal jacket (18). This arrangement prevents any dents caused
by the buckling of the outer metal jacket (18) while being crimped, and
allows dry cells to be more efficiently produced.
| Inventors:
|
Dokyu; Tensaburo (Hirakata, JP);
Sakamoto; Akio (Chigasaki, JP);
Ogino; Keiji (Katano, JP)
|
| Assignee:
|
Matsushita Electric Industrial Co., Ltd. (Osaka, JP)
|
| Appl. No.:
|
269956 |
| Filed:
|
April 8, 1999 |
| PCT Filed:
|
September 3, 1997
|
| PCT NO:
|
PCT/JP97/03093
|
| 371 Date:
|
April 8, 1999
|
| 102(e) Date:
|
April 8, 1999
|
| PCT PUB.NO.:
|
WO99/12218 |
| PCT PUB. Date:
|
March 11, 1999 |
| Current U.S. Class: |
429/168; 29/623.1; 29/623.2; 429/171; 429/172 |
| Intern'l Class: |
H01M 002/02; H01M 002/08; H01M 006/00 |
| Field of Search: |
29/623.1,623.2
429/164,166,168,171,172,94
|
References Cited
U.S. Patent Documents
| 3627586 | Dec., 1971 | Jammet | 136/107.
|
| 3630783 | Dec., 1971 | Przybyla | 136/107.
|
| 3660168 | May., 1972 | Ralston et al. | 136/107.
|
| 3859137 | Jan., 1975 | Jammet | 136/107.
|
| 4227701 | Oct., 1980 | Tsuchida et al. | 227/12.
|
| 4722874 | Feb., 1988 | Marchak | 429/56.
|
| 4965149 | Oct., 1990 | Ashihara et al.
| |
| Foreign Patent Documents |
| 0333023A1 | Sep., 1989 | EP.
| |
| 48-14812 | May., 1973 | JP.
| |
| 54-139845 | Oct., 1979 | JP.
| |
| 63-3056 | Jan., 1988 | JP.
| |
| 63-14360 | Jan., 1988 | JP.
| |
Primary Examiner: Shaw; Clifford C.
Assistant Examiner: Cooke; Colleen P.
Attorney, Agent or Firm: Jordan and Hamburg LLP
Claims
What is claimed is:
1. A dry cell including a cylindrical cell member and an outer metal jacket
for encasing the cell member, the metal jacket being formed by rolling a
metal jacket blank of a rectangular metal strip into a cylindrical shape
to cause opposing side edges of the metal strip to abut each other and
form an abutment joint and by inwardly curling and crimping a lower end of
the blank to make a bottom, the cell member being sealed in the metal
jacket by inwardly curling and crimping an upper end of the metal jacket,
wherein:
the metal jacket blank is provided with notches at both corners of a first
side edge of the side edges where the abutment joint is formed; and
the notches are respectively adjoined to an upper end and a lower end of a
second side edge of the side edges of the metal jacket blank forming a
curled abutment joint in a direction which is different from a radial
direction of the metal jacket.
2. A dry cell according to claim 1, wherein the width of the notches of the
metal jacket blank is substantially equal to a length of upper and lower
edges of the metal jacket blank situated between a line in the radial
direction aligning with the abutment joint and a line in the direction of
the curled abutment joint.
3. A method of producing a dry cell outer metal jacket for encasing a cell
member therein, comprising the steps of:
cutting a rectangular sheet of a metallic material along lines at equal
intervals and parallel to one side of the sheet to form a plurality of
rectangular first intermediate strips;
cutting the first intermediate strip along lines at equal intervals and
perpendicular to a lengthwise direction of the first intermediate strip to
form a plurality of rectangular second intermediate strips;
cutting the second intermediate strip into two pieces along a line in a
middle thereof and simultaneously removing from both edges at an
intersection of the line a substantially triangular shape at either end
along the line, so as to form a pair of metal jacket blanks of a same
shape having notches at upper and lower ends of a first side edge formed
by said cutting; and
rolling the blank into a cylindrical shape to cause the first side edge and
a second side edge, opposite the first side edge, to abut each other and
inwardly curling and crimping the lower end of the cylindrical blank to
make a bottom.
4. A method of producing a dry cell outer metal jacket according to claim
3, wherein the second intermediate strip is divided into the two metal
jacket blanks by a press cutting action with a punching tool which
comprises a slit forming portion having a width of about 1 mm and a pair
of substantially triangular notch forming portions connected uniformly to
the ends of the slit forming portion.
5. A method of producing a dry cell outer metal jacket according to claim 3
or 4, wherein the upper end of the metal jacket is inwardly curled and
crimped after a cell member having a cylindrical shape is loaded into the
metal jacket from an upper opening thereof to complete a dry cell.
6. A dry cell according to claim 1, wherein the notches are straight.
7. A dry cell according to claim 1, wherein the notches are convex.
8. A dry cell according to claim 1, wherein the notches are concave.
9. A dry cell comprising
a substantially cylindrical cell member; and
a substantially cylindrical outer metal jacket encasing said cell member,
said outer metal jacket comprising a metal jacket blank having first and
second side edges abutting one another to form an abutment joint and
notches only at both corners of said first side edge, upper and lower ends
of said metal jacket blank being inwardly curled and crimped such that
said notches of said first side edge adjoin an upper and lower end of said
second side edge and form curled abutment joints in directions different
than a radial direction of said outer metal jacket and said cell member is
sealed in said outer metal jacket.
10. A dry cell according to claim 9, wherein said notches have a width
substantially equal to a length of upper and lower edges of said metal
jacket blank situated between a line in the radial direction aligning with
said abutment joint and a line in the direction of a respective one of
said curled abutment joints.
11. A dry cell according to claim 9, wherein said notches are straight.
12. A dry cell according to claim 9, wherein said notches are convex.
13. A dry cell according to claim 9, wherein said notches are concave.
14. A method for producing a dry cell outer metal jacket for encasing a
cell member, comprising the steps of:
cutting a rectangular sheet of a metallic material at equal intervals and
parallel to one side of the sheet to form a plurality of rectangular first
intermediate strips;
cutting the first intermediate strip at equal intervals and perpendicular
to a lengthwise direction of the first intermediate strip to form a
plurality of rectangular second intermediate strips;
cutting the second intermediate strip into two pieces along a line in the
middle and removing a substantially triangular portion from each end of
the second intermediate strip along the line to thereby form a pair of
metal jacket blanks having the same shape and including notches at upper
and lower ends of only one side edge; and
rolling the blank into a cylindrical shape to cause opposite side edges to
abut each other and inwardly curling and crimping the lower end of the
cylindrical blank to make a bottom.
15. A method of producing a dry cell outer metal jacket according to claim
14, wherein the second intermediate strip is cut and the triangular
portions are removed from each end of the second intermediate strip at the
same time.
16. A method for producing a dry cell outer metal jacket according to claim
14, further comprising the step of using a press cutter to cut the second
intermediate strip into two pieces.
17. A method for producing a dry cell outer metal jacket according to claim
14, further comprising the step of using a punching tool providing a press
cutting action to cut the second intermediate strip into two pieces.
18. A method for producing a dry cell outer metal jacket according to claim
17, further comprising the step of providing the punching tool with a slit
forming portion and a pair of substantially triangular notch forming
portions connected to ends of the slit forming portion.
19. A method for producing a dry cell outer metal jacket according to claim
14, further comprising the step of inwardly curling and crimping an upper
end of the metal jacket after a cell member having a cylindrical shape is
loaded into the metal jacket from an upper opening thereof to complete a
dry cell.
Description
BACKGROUND
The present invention relates to a dry cell which is relatively small in
size and has a cylindrical appearance and to a method of manufacturing an
outer metal jacket of the dry cell.
Since the material for outer jackets of a small cylindrical dry cell was
changed from paper to metal, its ability to prevent leakage has been
improved thus increasing the performance of the dry cell. Such a metallic
outer jacket of a dry cell (referred to as simply an outer metal jacket)
is commonly fabricated in such a producing process as shown in FIG. 6. The
procedure starts with cutting a hoop material of about 0.2 mm thickness
made of tin-plated steel into rectangular base sheets 1 of predetermined
dimensions, for example 785 mm wide and 850 mm long, as shown in FIG.
6(a). This is followed by slitting and trimming two edges of about 2 mm
width along both opposing sides of the base sheet 1. After removing the
two edge pieces 2, slits are formed which are equally spaced and parallel
to the sides of the base sheet 1 as denoted by the two-dot chain lines in
FIG. 6(b). The base sheet 1 is then cut along these slits into a group of
intermediate strips 3 as shown in FIG. 6(c). Each intermediate strip 3 is
punched out with a blanking die as shown in FIG. 6(d), thus producing a
number of metal jacket blanks 4, one of which is shown in FIG. 6(e).
The metal jacket blank 4 is then rolled to a cylindrical shape as shown in
FIG. 6(f). While two side edges 4a and 4b of the blank 4 are adjoined to
each other, a base 4c is inwardly crimped to form a bottom 5, thus making
a cylindrical outer metal jacket 7 with a bottom. The outer metal jacket 7
is loaded through the open end thereof with a cell member which comprises
a power generating element filled in a zinc can and is coated with an
insulating tube. The upper end 4d of the outer metal jacket 7 is then
inwardly crimped to be pressed via an insulating ring against the shoulder
of the cell member, thus producing a small cylindrical dry cell 8 as shown
in FIG. 5.
The rectangular blank 4 punched out from the intermediate strip 3 has
notches 9a, 9b at four corners thereof formed by removing triangular
segments as shown in FIG. 6(e). When the blank 4 is rolled and its base 4c
is crimped inwardly or its upper end 4d is crimped inwardly with the cell
member loaded therein, each pair of notches 9a or 9b, at the upper or
lower side are adjoined to each other along a joint 10 between the two
side edges 4a and 4b or in the radial direction R of the outer metal
jacket 7, forming a curled abutment joint 11 as shown in FIG. 5.
More specifically, for forming the curled abutment joint 11, the periphery
of the outer metal jacket 7 at its upper end is pressed into a specific
semicylindrical curling mold which has a curved cross section. As the
upper end of the outer metal jacket 7 is gradually bent to form an even
curve all around its periphery, the opposing notches 9aare steadily
adjoined to each other from the outer side to the inner side. When the
notches 9a are bent to abut each other, a considerable amount of stress is
locally exerted along the curled abutment joint 11 and the bending stress
is concentrated thereon thus causing buckling.
Further, the cell member loaded in the outer metal jacket 7 varies in
height. If the cell member is short, an extra stress is given after the
two notches 9a are attached to each other to form the curled abutment
joint 11. Such locally concentrated bending stress causes dents 12 on
either side of the abutment joint as shown in FIG. 5, which damage the
appearance of the outer metal jacket 7. Also, the two notches 9a are
fixedly pressed against each other along the curled abutment joint 11,
thus firmly pressing a seal member of the cell, which may obstruct the
discharge of a gas from the cell in case the gas pressure inside the cell
8 soars unexpectedly.
In order buckling, an improved cylindrical dry cell has been proposed in
which four corners of an outer metal jacket blank at upper and lower ends
of both sides are rounded off by removing segments of different lengths or
heights which are determined in a specific ratio (as disclosed in Japanese
Utility-model Publication No. 1-19053). However, it is necessary to cut
the blank of the cylindrical dry cell to a desired shape under precise
control of the blanking operation. Especially for producing dry cells of
small size, it is difficult to precisely control the configuration of tiny
blanks when punching them out. On the other hand, the outer metal jacket
for dry cells of larger size is jointed by laser welding, whereby the
buckling is prevented. However, laser welding is generally not utilized
for producing small dry cells because of its low productivity and high
producing cost.
In order to form the small notches 9a, 9b having a desired configuration at
four corners of the metal jacket blanks 4 in the production process of the
outer metal jacket 7 described above, there is virtually no alternative
but to punch out a plurality of blanks 4 from the rectangular intermediate
strip 3 which is slightly greater in width than a pair of blanks 4
arranged side by side as shown in FIG. 6(d). When the dry cell is large in
overall size, the notches may be provided by cutting off four corners of a
rectangular strip. However, the notches 9a, 9b of the blank 4 for smaller
dry cells are normally minute, i.e., have a height h of 2.2 mm along the
sides 4a and 4b and a width d of 0.35 mm from the sides 4a and 4b. The
cutting tool of the cutting machine for providing such minute notches 9a,
9b must be extremely sharp and has a short life. Moreover, it is
impossible in practice to securely hold a tiny metal jacket blank 4
precisely at a given position.
Accordingly, a waste of material is left in a large amount after the
intermediate strip 3 is punched out as can be seen from FIG. 6(d). The
number of the blanks 4 punched out from the intermediate strip 3 is
limited thus being inefficient in production. In light of the mass
production of small dry cells in recent years, such method as described
above which creates the loss of material is unfavorable from the
economical point of view.
It is thus an object of the present invention to provide a dry cell having
such a configuration that any dents caused by the buckling when crimped is
effectively prevented, and a method of producing the outer metal jackets
efficiently.
SUMMARY OF THE INVENTION
In order to solve the above described problems, a dry cell of the present
invention is comprised of a cylindrical cell member and an outer metal
jacket for encasing the cell member, the metal jacket being formed by
rolling a metal jacket blank of a rectangular metal strip into a
cylindrical shape to cause the opposing side edges thereof to abut each
other and by inwardly curling and crimping a lower end of the blank to
make a bottom, the cell member being sealed in the metal jacket by
inwardly curling and crimping an upper end of the metal jacket. The metal
jacket blank is provided with notches at both corners of one side edge
thereof where the abutment joint is formed, and the notches are
respectively adjoined to an upper end and a lower end of the other side
edge of the blank, forming a curled abutment joint along a direction which
is different from the radial direction of the metal jacket.
The blank for the metal jacket has notches at the upper and lower ends of
only one side thereof. Thus, the upper and lower notches come into direct
contact with their corresponding edges of the other side at the very end
of the curling action. As the notches come to join with the other end to
form the curled abutment joint at the very end of the curling action, the
bending stress is not concentrated locally to the curled abutment joint,
thus creating no dents caused by the buckling.
It is preferable that the width of the notches at one side edge of the
metal jacket blank is determined to correspond with the other side edge
which exceeds a line along the radial direction at both ends of the
cylindrical metal jacket.
This permits the two notches at the side edge of the blank to be adjoined
to their respective upper and lower ends of the other side without making
gaps. The curled abutment joint of a favorable configuration can be
formed, contributing to a better appearance of the dry cell.
A method of producing a dry cell outer metal jacket for encasing a cell
member therein according to the present invention comprises the steps of:
cutting a rectangular sheet of a metallic material along the lines at
equal intervals parallel to one side of the sheet to form a plurality of
first intermediate strips of a rectangular shape; cutting the first
intermediate strip along the lines at equal intervals perpendicular to the
lengthwise direction to form a plurality of second intermediate strips of
a rectangular shape; cutting the second intermediate strip with a press
cutter into two pieces along a line in the middle and at the same time
removing both edges of substantially a triangular shape at either end
along the line, so as to form a pair of metal jacket blanks of the same
shape respectively having notches at upper and lower ends of only one side
edge thereof; and rolling the blank into a cylindrical shape to cause two
opposite sides to abut each other and inwardly curling and crimping the
lower end of the cylindrical blank to make a bottom.
According to such method of producing the outer metal jackets, the notches
can be readily and quickly provided at both upper and lower edges of only
one side edge of the metal jacket blank when dividing the second
intermediate strips into two blanks in the punching process. This is
because the second intermediate strip can be secured at both sides of the
cutting line when being punched, and because it is unnecessary to provide
notches at upper and lower edges of the other side of the blank as in the
prior art.
As compared with the conventional method in which a group of intermediate
blanks of a rectangular shape are punched out from a material sheet, the
method of the present invention minimizes the waste of material after the
blanks are punched and rolled to the metal jackets. The number of the
blanks cut out from the material sheet is increased thus improving the
efficiency of production. Since the dry cells are produced in great
quantity, greater economy of material can be attained.
It is preferable that the second intermediate strip is divided into the two
metal jacket blanks by the press cutting action with a punching tool which
comprises a slit forming portion having a width of about 1 mm and a pair
of substantially triangular notch forming portions connected uniformly to
either end of the slit forming portion. The life of the punching tool can
be lengthened due to such configuration.
The dry cell according to the present invention can be readily produced by
the method of the present invention, in which the upper end of the outer
metal jacket is inwardly curled and crimped after a cell member of a
cylindrical shape is loaded into the metal jacket from the upper opening
thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1(a)-1(d) illustrate a dry cell according to one embodiment of the
present invention, in which
FIG. 1(a) is a perspective view of an upper part of the dry cell,
FIG. 1(b) is a plan view of the same,
FIG. 1(c) is a half cut-away longitudinal cross sectional view of the same,
and
FIG. 1(d) is a front view of a blank of an outer metal jacket;
FIGS. 2(a)-2(g) show steps of producing the outer metal jacket of the dry
cell;
FIG. 3 is a half longitudinal cross sectional view of a mold designed for
crimping the outer metal jacket;
FIGS. 4(a) and 4(b) are front views showing modifications of the blank;
FIG. 5 is a perspective view of a conventional dry cell; and
FIGS. 6(a)-6(f) show steps of producing the outer metal jacket of the
conventional dry cell.
DETAILED DESCRIPTION
Preferred embodiments of the present invention will be described in details
referring to the accompanying drawings. FIGS. 1(a)-1(d) illustrate a dry
cell 17 according to the embodiment of the present invention, in which
FIG. 1(a) is a perspective view of an upper part of the dry cell, FIG.
1(b) is a plan view of the same, FIG. 1(c) is a half cut-away longitudinal
cross sectional view of the same, and FIG. 1(d) is a front view of a blank
19 of an outer metal jacket 18 of the dry cell 17. A characteristic of
this dry cell 17 is that its curled abutment joint 20 is formed at upper
and lower ends of the outer metal jacket 18 along a direction S which is
different from the radial direction R of the metal jacket 18 as shown in
FIGS. 1(a) and 1(b). The blank 19 for the metal jacket 18 has notches 21a
and 21b at only two corners thereof between one side 19a and an upper and
lower sides 19c, 19d, and the other side 19b is not provided with any
notches as best shown in FIG. 1(d). Since the two notches 21a and 21b are
formed on one side 19a of the blank 19, the width 2d of the notches is two
times greater than that of the conventional notches while the height h
which is equal to an inward curling margin of the metal jacket 18 remains
the same.
The structure of the dry cell 17 is now explained. As shown in FIG. 1(c), a
separator 23 impregnated with an electrolyte is fixedly disposed to the
inner wall of an anode zinc can 22 of a cylindrical shape with a bottom,
and filled with a cathode active material or a cathode mixture 24. A
carbon electrode 27 serving as a collector is extended through the center
of the cathode mixture 24. The upper opening of the anode zinc can 22 is
hermetically sealed with a seal member 28 through which the carbon
electrode 27 penetrates. The bottom face of the anode zinc can 22 is
capped with a negative terminal plate 29, while the protruding upper end
of the carbon electrode 27 is capped with a positive terminal plate 30.
The cathode mixture 24 may be made of a mixture of an active material such
as manganese dioxide and a conductive material such as acetylene black or
graphite added with an electrolyte, and is compressed into a cylindrical
form and tightly pressed around the carbon electrode 27. The cathode
mixture 24 is wrapped with the separator 23 and loaded in the anode zinc
can 22, which is then coated with an insulating tube 31 thus constituting
a cell member 26. The cell member 26 is inserted into the outer metal
jacket 18 which is crimped at the upper end thereof and fixedly
accommodated in the metal jacket 18 with an upper insulating ring 52
inserted therebetween. The reference numeral 53 denotes a lower seal ring.
The procedure of manufacturing the outer metal jacket 18 of the dry cell 17
will be explained referring to FIGS. 2(a)-2(g) which shows the steps in
producing order. As shown in FIG. 2(a), a hoop material made of tin-plated
steel being about 0.2 mm in thickness is cut into rectangular sheets 1 of
given dimensions similarly with the prior art. The sheet 1 is then cut
with a slitter along the cutting lines denoted by the two-dot parallel
chain lines and divided into a pair of edge strips 32 of about 2 mm wide
and a given number of first intermediate strips 33 of a rectangular shape
parallel to the edge strips 32, as shown in FIG. 2(b). The first
intermediate strip 33 is trimmed at both lengthwise ends by slitting and
cut along a group of parallel cutting lines which cross at right angles
with the lengthwise direction to obtain second intermediate strips 34 of a
smaller rectangular shape, as shown in FIG. 2(c). The length of the second
intermediate strip 34 is 1 mm longer than that of the two blanks 19
arranged adjacent to each other.
As shown in FIG. 2(d), the second intermediate strip 34 is separated into
two metal jacket blanks 19 as shown in FIG. 2(e) or FIG. 1(d) with a
punching tool 37 by cutting at right angles with respect to the lengthwise
direction at its center. The punching tool 37 comprises a slit forming
portion 37a for making a cutting slit of about 1 mm wide and a pair of
substantially triangular notch forming portions 37b and 37c connected to
either end of the slit forming portion 37a. Each end of the notch forming
portions 37b and 37c is greatest in width which is equal to a sum of two
times the width 2d of the notch 21 and the 1 mm width of the slit forming
portion 37a. Accordingly, the notch forming portions 37b and 37c of the
punching tool 37 are of greater size for cutting a couple of the notches
21, of which width 2d is two times greater than that of the notch 9 in the
conventional method.
As compared with the conventional method in which the metal jacket blanks 4
are punched out from the intermediate strip 3 (FIG. 6), the blanks 19 are
obtained by punching each of the group of second intermediate strips 34
which are divided from the first intermediate strip 33 in this embodiment.
The waste of material in the cutting of the blanks 19 is thus decreased to
about 1/4 of that in the conventional method of producing the outer metal
jacket 18. The number of the blanks 19 cut out from the given size of the
sheet 1 is increased, enhancing the productivity accordingly. The
productivity was increased by about 6 percent according to experiments as
compared with the prior art. This increase will yield various economical
merits since the small dry cells are manufactured in a great amount
recently.
It is inevitable that burrs 38 are created on both sides of the blanks as
shown in FIG. 2(f) in the cutting process to form the slits shown in FIGS.
2(b) and 2(c) and in the punching process to divide the strips into blanks
with the punching tool 37 as shown in FIG. 2(d). A step shown in FIG. 2(f)
for pounding the burrs is thus provided in which the blank 19 is placed on
a bed 40 and vertically hammered with burr hammers 39 to remove the burrs
38.
After the burrs 38 are removed, the blank 19 is rolled so that its sides
19a and 19b are abutted each other as shown in FIG. 2(g). Further, the
lower end 19c is inwardly curled to make the cylindrical outer metal
jacket 18 with a bottom. The cell member 26 is loaded into the metal
jacket 18 with the upper insulating ring 52 and the lower seal ring 53 as
shown in FIG. 1(c). The upper end 19d of the metal jacket 18 is then
inwardly crimped to press the edge of the metal jacket 18 onto the
terminal surface of the cell member 26, with the upper insulating ring 52
firmly placed therebetween, completing the small cylindrical dry cell 17
as shown in FIG. 1(c).
For crimping the upper end 19d of the outer metal jacket 18, a mold 41
shown in FIG. 3 is used. FIG. 3 illustrates a longitudinal cross section
of one half of the mold 41 of a cylindrical shape. The mold 41 has a
pre-bending surface 41b extending upwardly and obliquely from a bending
start end 41a toward the center and a bending surface 41c curving from the
upper end of the pre-bending surface 41b downwardly to the center. The
upper end 19d of the metal jacket 18 loaded with the cell member 26 is
curled by being firmly pressed into the mold 41 from below. Denoted by the
two dot chain line is the configuration of the mold P in the prior art for
comparison with the present invention.
The blank 19 for the outer metal jacket 18 has the notches 21 at the upper
and lower ends of only one side edge 19a thereof. Thus, the upper and
lower notches 21a and 21b come into direct contact with their
corresponding edges of the other side edge 19b at the very end of the
curling action. As it is not necessary to gradually adjoin the notches of
the blank from the outer side toward the inner side as in the prior art
arrangement, the upper end 19c is freely curled along the pre-bending
surface 41b towards the center of the mold 41, and the notches come to
join with the other end 19b to form the curled abutment join 20 at the
very end of the curling action. The bending stress is thus not
concentrated locally to the curled abutment joint 20, thus creating no
dents caused by the buckling.
Of the curled abutment joint 20, one side edge 20a having the notch 21a is
less rigid than the other side edge 20b without the notch. In case that
the gas pressure inside the cell soars unexpectedly, the side edge 20a is
more prone to curl up on receipt of the gas pressure, creating a gap,
through which the gas can escape to the outside. The dry cell according to
the present invention thus has improved performance of preventing
explosions.
The notches 21a and 21b are not limited to the straight configuration as
has been described but may be formed in any appropriate shapes such as an
outwardly curved convexed notch 42 or an inwardly curved concaved notch 43
as shown in FIGS. 4(a) and 4(b). In either case, the width of the notches
42 and 43 is set to be two times greater than the width d of the prior art
in which notches are provided at both edges of the blank.
According to the method of producing the outer metal jacket 18 of the
present invention, the yield of products was increased by about 9 percent
as compared with the conventional method hence considerably contributing
to economical profits.
As set forth above, the present invention is advantageous in producing dry
cells or outer metal jackets of the dry cells more efficiently and
productively.
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